The optical connection between an optical device such as an optical waveguide component, an optical semiconductor device (LD array, LED array), etc. and optical fiber has so far been made by the following procedure. An optical fiber end portion, in which a plurality of optical fibers are arranged at predetermined intervals, is butted against an optical device, or the optical fiber end portion and the optical device are disposed in opposition to each other. Then, alignment is performed to align optical axes between the optical fiber and the optical device. After that, both elements are bonded by an adhesive such as a heat curing type or a light (ultraviolet rays) curing type. Alternatively, an optical fiber end portion and an optical device are opposed to each other with a predetermined gap between them, optical axes are aligned between the optical fiber and the optical device, and then the optical fiber end portion and the optical device are welded to a metal base.
As a first example of such a connection between an optical fiber end portion and an optical device, for example, the connection between an optical fiber end portion and an optical waveguide component is known.
The optical fiber end portion has a tape fiber, in which a plurality of optical fibers are arranged at predetermined intervals in a coating, and a ferrule. The ferrule has a butting end face, which is disposed in opposition to or butted against an optical waveguide component, and a plurality of fiber holes formed in parallel at predetermined intervals. One end of the optical fiber is inserted into each of the fiber holes and bonded, and the optical fiber is exposed to the butting end face. The most inexpensive and general method for manufacturing the ferrule is plastic molding performed by using a mold.
The optical waveguide component consists of a waveguide substrate and a waveguide layer, and sometimes a cover is bonded onto the waveguide layer. In the waveguide layer, single or plural waveguides are formed, and the waveguides are exposed to the butting end face at both ends. The cover serves to ensure an effective area for bonding to the optical fiber end portion by making the area and shape of the butting end face of the optical waveguide component substantially equal to those of the butting end face of the optical fiber end portion.
The aforementioned optical fiber end portion is butted against the optical waveguide component through their butting end faces, and is bonded to the optical waveguide component after alignment is performed between each optical fiber and the corresponding waveguide.
When the optical fiber end portion is bonded to the optical waveguide component, it is necessary to align the optical fiber and the corresponding waveguide on the order of submicrons, and to bond and fix the optical fiber end portion to the optical waveguide component in a short period of time while maintaining the aligned condition in order to minimize the connection loss at the optical fiber end, particularly for optical fiber of single mode.
As the bonding means, a heat curing type adhesive such as epoxy resin, which cures at a high speed, is used. The optical fiber end portion is bonded to the optical waveguide component at portions excluding the portion where the optical fibers and waveguides are exposed to the butting end face to prevent the interruption of the optical path between each optical fiber and the corresponding waveguide.
As a second example, the connection of another construction between the optical fiber end portion and the optical waveguide component is also known.
This optical fiber end portion has a tape fiber, a V-grooved base plate, and a press cover, and a butting end face is formed at each end thereof. The tape fiber has a plurality of optical fibers arranged at predetermined intervals in a coating. The end portion of each optical fiber is exposed by removing the coating from the end portion of the optical fiber. The exposed end portion of each optical fiber is positioned by each V groove formed in the V-grooved base plate, and each optical fiber is fixed to the V-grooved base plate by a press cover.
The end face of the optical fiber is exposed to the butting end face, and is polished together with the V-grooved base plate and the press cover. The V-grooved base plate and the press cover are made of an optically transparent material such as glass.
The optical waveguide component is configured in a similar way to the optical waveguide component of the aforementioned first example, and the cover is made of an optically transparent material such as glass.
The optical fiber end portion is butted against the optical waveguide component through their butting end faces, and is bonded to the optical waveguide component with a light curing type adhesive while irradiating light (ultraviolet rays) after alignment is performed between each optical fiber and the corresponding waveguide.
In this process, since the V-grooved base plate and the press cover are made of an optically transparent material, the transmitting ultraviolet rays cure the adhesive in a shorter period of time as compared with the aforementioned heat curing type adhesive such as epoxy resin, which cures at a high speed. Therefore, the optical fiber end portion is bonded to the optical waveguide component rapidly at the butting end face.
Further, as a third example, the connection between the optical fiber end portion of the above second example and an optical semiconductor is also known.
The optical semiconductor has a heat sink arranged between an LD array, in which a plurality of laser diode elements are arranged in line, and a carrier. Each laser diode element is electrically connected to the carrier with a bonding wire, and the carrier is fixed to a metallic mount base.
On the other hand, the optical fiber end portion is welded to a metallic base via a sub-base. Each optical fiber in the tape fiber is aligned with the corresponding laser diode element, and the base is welded to the mount base.
The above-described connections between the optical fiber end portion and the optical device pose problems described below.
First, in the connection between the optical fiber end portion and the optical waveguide component as described in the first example, for example, when the optical waveguide component is silica-type one in which silica-type waveguide layer is formed on a silicon substrate, the optical waveguide component has a linear expansion coefficient of about 2.4.times.10.sup.-6 at about 20.degree. C. For the optical fiber end portion, the linear expansion coefficient of plastic material forming the ferrule is, for example, 5.times.10.sup.-6 or more at about 20.degree. C. when the material is an epoxy resin containing fine particles of silicon dioxide (SiO.sub.2) as a filler.
For this reason, after the optical fiber end portion is connected to the optical waveguide component, the difference in linear expansion coefficient between these elements caused by a temperature change with time in the working environment disturbs the aligned condition between each waveguide and optical fiber, resulting in the decrease in performance such as increase in connection loss and the loss of function.
The ferrule of the optical fiber end portion is manufactured by plastic molding using a mold. Therefore, if the linear expansion coefficient in the direction in which a plurality of fiber holes are arranged differs from the linear expansion coefficient in the direction perpendicular to the arranging direction, deformation such as a warp is produced on the ferrule, so that fiber holes cannot be formed with high accuracy.
Further, the ferrule of the optical fiber end portion has so far used an optically opaque material by containing filler etc. in an epoxy resin to decrease the linear expansion coefficient and improve the strength and dimensional accuracy. Therefore, it has been very difficult to connect the conventional optical fiber end portion to the optical waveguide component by using a light curing type adhesive.
For the optical fiber end portions described in the second and third examples, an optically transparent material such as silicon and ceramics as well as the aforementioned glass can be used as a material for the V-grooved base plate and press cover.
However, since glass, silicon, and ceramics are hard and brittle, it is difficult to grind the V grooves, and the polishing property of the butting end face is poor, so that the machining cost is high.
Also, the optical fiber end portion is assembled by positioning fine optical fibers by the V grooves and by fixing optical fibers to the V-grooved base plate by using the press cover, so that the workability in assembly is poor.
Moreover, since the construction is such that the optical fibers are fixed by the press cover, if the press cover presses the optical fibers excessively, the optical fiber is broken easily when a stress acts on the optical fiber extending from the V-grooved base plate.
This invention was made to solve the above problems. Accordingly, an object of the present invention is to provide an optical fiber end portion which can be formed with high accuracy and therefore can be connected to an optical device accurately, a method for manufacturing such optical fiber end portions, and construction for connecting the end portion to an optical device.
Another object of the present invention is to provide an optical fiber end portion which can be manufactured easily at a low cost and in which optical fibers are less prone to be broken, a method for manufacturing such optical fiber end portions, and construction for connecting the end portion to an optical device.